The present invention pertains to a laminator or combiner for forming corrugated paperboard sheets from a single face web and discrete cover sheets and, more particularly, to such a system utilizing cover sheets which comprise serially fed pre-printed labels.
It has not been practical or possible to utilize the full capabilities of modern printing equipment to print and/or decorate the outside face of a corrugated paperboard carton blank made in a conventional double face corrugating system. The basic reason for the difficulty is the need to use a web-fed printer to print the single face web which is to become the outside liner of the corrugated boxes made from the double face corrugated web. It has long been recognized that, if the outside liner for the corrugated carton blanks could be made from discrete pre-printed sheets, the enhanced versatility of sheet-fed printers could be used to provide printed cartons with virtually any desired pattern of printing and/or decoration. Such a process would thus apply serially fed pre-printed cover sheets or labels to be joined to the exposed flute tips of a single face corrugated web by passing the two between a laminating roll, with a suitable adhesive having been applied upstream to the flute tips.
U.S. Pat. No. 3,591,436 operates by feeding pre-printed sheets in end-to-end abutment or, preferably, with their adjacent edges overlapping slightly into a laminating nip through which a glued single face adhesive web is also passing, such that the printed sheets complete the formation of a substantially continuous double face corrugated web. The use of conventional starch-based paperboard adhesive requires the double face web to be passed through a drying section, after which individual double face corrugated sheets are cut by passing the web through a rotary cut-off knife operated in response to marks on the pre-printed labels. Edge-to-edge abutment or slight overlap of the pre-printed sheets is important to prevent exposure of glued flute tips on the single face web.
U.S. Pat. No. 3,775,211 shows another laminating system in which pre-printed labels or cover sheets are fed into contact with the pre-glued flute tips of a single face web and joined thereto by passage through a laminating nip. However, unlike the system of the previously described patent, the single face web is cut immediately after the leading edge of the web and corresponding leading edge of the cover sheet have entered the laminating nip. Thus, a completed double face corrugated sheet, cut to length, exits from the laminating nip. Synchronization of the leading edge of the printed cover sheet to cause it to slightly overlap the leading edge of the single face web is also provided to avoid exposed adhesive on the underlying single face web. The cover sheets are fed in an overlapping or shingled relation and each sheet is momentarily stopped just upstream of the laminating nip and released by a mechanically operated timing mechanism to coordinate the desired leading edge coordination with the single face web.
In actual operation, these prior art systems cannot adequately deal with problems caused by cover sheet slippage, variations in nominal sheet length, and cumulative error problems caused by these and other factors. A laminating system which could accurately and effectively overcome these problems would be most desirable.
In accordance with the present invention, a method and apparatus are provided for rapid and accurate lamination of pre-printed cover sheets to a single face web in which the sheets are fed non-stop into a laminating nip and the single face web is custom cut to accurately match the trailing edge of the cover sheet and to compensate for variations in leading edge match of the two components entering the laminating nip and variations in the length of the cover sheet.
A presently preferred method for laminating discrete rectangular cover sheets to a single face corrugated web which web is severed into cut length portions to form, with the cover sheets, double face corrugated sheets includes the steps of feeding cover sheets in serially spaced relation from a cover sheet supply non-stop into a downstream laminating nip; feeding the single face web from a web source, through a cut-off knife positioned less than one sheet length from the laminating nip, and into said nip; passing each cover sheet through a variable speed positioning nip located less than one sheet length upstream of the laminating nip; controlling the speed of the positioning nip to cause the leading edge of the cover sheet traveling therein to extend at least to the leading edge of the web entering the laminating nip; sensing the position of the trailing edge of the cover sheet which is in the positioning nip; operating the cut-off knife in response to the sensed position of the trailing edge of the cover sheet to sever the web into a cut length portion such that the trailing edge of the cover sheet extends, in the upstream direction, at least to the trailing edge of the single face cut length portion; and, passing the cover sheet and cut length portion of the web through the laminating nip to form the double face corrugated sheet.
In a broad sense, the step of controlling the speed of the positioning nip may be used to provide any desired position of the leading edge of the cover sheet with respect to the leading edge of the web in a range from a direct edge-to-edge match to a maximum acceptable overlap of the cover sheet leading edge. Similarly, the operation of the cut-off knife in response to the sensed position of the cover sheet trailing edge may be utilized to provide a desired position of the cover sheet trailing edge with respect to the trailing edge of the cut length of single face in a range from direct edge-to-edge match to a maximum acceptable cover sheet trailing edge overlap.
The method of the present invention also preferably includes the step of applying an adhesive to the exposed flute tips of the corrugated web at a point upstream of the cut-off knife. The method also includes the step of guiding each cover sheet laterally during the feeding step to provide a desired position of alignment of the cover sheet side edges with respect to the lateral edges of the single face web. The method is particularly adapted to utilize cover sheets which comprise pre-printed labels.
Correspondingly, the apparatus for practicing the method of the present invention comprises means for feeding cover sheets in spaced relation and without stop from a sheet supply into a downstream laminating nip; means for feeding the single face web from a source, through a cut-off knife which is positioned less than one sheet length from the laminating nip, and into that nip; means located in the feed path of the cover sheets and positioned less than one sheet length upstream of the laminating nip for varying the speed of the cover sheet which is passing through the speed varying means; means for controlling the operation of the speed varying means to cause the leading edge of the cover sheet to extend at least to the leading edge of the web entering the laminating nip; means for sensing the position of the cover sheet trailing edge as it passes through the speed varying means; means for operating the cut-off knife in response to the sensed position of the cover sheet trailing edge to sever the web into a cut length portion such that the trailing edge of the cover sheet extends upstream at least to the severed trailing edge of the single face cut length portion; and means for passing the cover sheet and cut length portion of the web through the laminating nip to form the double face corrugated sheet. The speed varying means preferably comprises a variable speed positioning nip.